Saturated macrocyclic ketones having 14- to 18-membered rings, e.g. muscone (3-methylcyclopentadecanone), are sought-after fragrances or flavors. Since the compounds from natural sources are available only in small amounts, the synthesis of these has been the subject matter of comprehensive studies.
The preparation of muscone from 14-methylbicyclo[10.3.0]pentadecene[1(12)] has been known for a long time. Thus, CH-503 680 and U.S. Pat. No. 3,778,483 describe a process for preparing muscone, in which 14-methylbicyclo[10.3.0]pentadecene[1(12)] is oxidized by means of ozone to cleave the central double bond, a keto group of the resulting diketone is reduced to the alcohol and the unsaturated macrocyclic ketone obtained after elimination of water is hydrogenated to muscone.
V. Rautenstrauch et al., Helv. Chim. Acta Vol. 73, (1990), p. 896, describe a synthesis of muscone which starts out from 2-(2′-methylprop-2′-enyl)cyclododecan-1-one and proceeds via (3aRS,13aSR)-3a,4,5,6,7,8,9,10,11,12,13,13a-dodecahydro-2-methyl-1H-cyclopentacyclododecen-13a-ol. Further syntheses of muscone are described in DE 1 668 054 and Helv. Chim. Acta Vol. 62, (1979), p. 2657.
However, owing to the reagents used, their complexity and/or the yields achieved, the known processes are unsatisfactory. It is an object of the invention to provide a process by means of which particular saturated ketones, in particular saturated macrocyclic ketones such as muscone, can be obtained industrially in a simple way.
The oxidation of olefins by means of N2O to form an aldehyde or a ketone is a reaction which has been known for a long time and is described, for example, in GB 649,680. WO 2008/000756 describes a process for preparing a cyclic ketone having from 7 to 16 carbon atoms, in which a cyclic alkene having from 7 to 16 carbon atoms and at least one C═C double bond is oxidized by means of dinitrogen monoxide.
Cleavage of the C═C double bond usually does not occur or occurs to only a minor extent in this reaction. The exception is some strained rings systems such as bicycloheptene or indene; see E. V. Starokon, Adv. Synth. Catal. 2004, 346, 268-274.
The oxidation of tetrasubstituted olefins by means of N2O has hitherto been described only for the example of tetramethylethene. There, no cleavage of the C═C double bond was observed, see Bridson-Jones et al., JCS (1951), 3009.